For working or walking surfaces, the open sides of upper levels should be?

For working or walking surfaces, it is essential that the open sides of upper levels are guarded to ensure the safety of individuals. Guarding typically involves the installation of railings or physical barriers that provide a protective barrier and reduce the risk of falls from elevated surfaces. This safety measure is a crucial aspect of workplace safety regulations and guidelines, such as those outlined by OSHA (Occupational Safety and Health Administration).

Guarding can prevent accidents that could result in serious injuries or fatalities, especially in environments like construction sites or industrial settings where workers may be at significant heights. Thus, the importance of having guardrails or barriers in place cannot be overstated, as they serve as a primary line of defense against falls.

While options like being unobstructed, secured, or labeled may have their place in certain safety protocols or procedures, they do not directly address the specific need for fall protection that guarding provides in this context. Guarding is a proactive measure that directly prevents the hazards associated with open sides of upper levels, making it the most appropriate choice.